1. Field of the Invention
This invention relates to an electrolytic solution for a clinometric sensor and, particularly, to an electrolytic solution sealed into a closed container of a clinometric sensor of potentiometric type. The present disclosure related to subject matter contained in Japanese Patent Application No. 9-124019 (filed on May 14, 1997), which is expressly incorporated herein by reference in its entirety.
2. Description of the Related Art
Conventionally, a clinometric sensor detecting the position of a bubble remaining in a liquid sealed into a closed container is used to detect the inclination of surveying equipment, aircraft, automobiles, and so on. As one of such a clinometric sensor, a potentiometric type is known in which an electrolytic solution is used as the liquid sealed into the closed container and which detects the position of a bubble by measuring variations in the resistance of the electrolytic solution.
In the clinometric sensor of potentiometric type, a pair of upper electrodes are formed on the upper inner surface of the closed container and a common electrode is formed on the bottom surface of the container. Constant voltages are applied between each of the upper electrodes and the common electrode. In this condition, when the closed container inclines to the direction in which detection of the angle of inclination is to be executed, the position of the bubble varies, so that the contact area of the electrolytic solution with the upper electrodes varies. This causes variations in the resistances between each of the upper electrodes and the common electrode whereby the ratio of the currents flowing through each of the upper electrodes is varied. This ratio of the currents is detected by a detecting circuit as a signal indicating the angle of inclination of the closed container. In this manner, the angle of inclination of the subject for measurement to which the clinometric sensor is attached can be measured.
Solvents used as the electrolytic solution for the clinometric sensor are, in turn, two types including a methanol-based type and N,N-dimethylformamide (DMF) based type. The methanol-based solvent is, for example, a mixture of methanol and water, and so on. The DMF-based solvent is, for example, a mixture of DMF and nPA (n-propanol), and so on.
The above solvents used as the electrolytic solution for the clinometric sensor however have the following drawbacks: Specifically, the DMF-based solvent has a viscosity higher than that of the methanol-based solvent and therefore it will take time for a bubble in an electrolytic solution to move. The use of the DMF-based solvent therefore gives rise to the problem wherein the response characteristics of the clinometric sensor (the speed of response of output to the angle of inclination when the clinometric sensor is inclined) is impaired.
On the other hand, the methanol-based solvent is lower in viscosity than the DMF-based solvent and hence has an advantage that the response characteristics of the clinometric sensor is higher than in the case of using the DMF-based solvent. However, it is known that some combinations of methanol and a halogenated compound (for example, KI and KCl) used as an electrolyte dissolve platinum and gold used as electrode materials though it depends on the sorts of halogenated compound. The use of the methanol-based solvent has the possibility of dissociation of electrodes. Also, when the methanol-based solvent is used, there is the case where the output of the clinometric sensor becomes unstable in a high temperature condition (at temperatures higher than 50.degree. C.).